A method for the inversion of flow channel and cave structure in fractured-vuggy reservoirs

Abstract

The application discloses a kind of fracture-cave type reservoir flow channel and cave structure inversion method, comprising the following steps: S1: establishing fracture-cave type reservoir oil-gas-water three-phase multicomponent flow mathematical model, obtains fracture-cave type reservoir fluid flow numerical simulation method;S2: construct inversion variable space, establish production dynamic fitting objective function;S3: extract multi-source data constraint information, and flow channel and cave structure inversion are carried out according to multi-source data constraint information.The beneficial effects of the present application are: not only can explain the geometric structure of flow channel and cave in fracture-cave type reservoir, but also can explain the flow property of flow channel and the effective volume space of cave, realize the dynamic connectivity analysis of flow channel and cave structure in fracture-cave type reservoir, and through the explanation of flow channel and cave structure and property, it can also provide scientific basis for developers, and can realize the efficient development of fracture-cave type oil and gas reservoir.

Description

Technical Field

[0001] This invention relates to the field of carbonate rock oil and gas development technology, and in particular to a method for inverting flow channels and cavern structures in fractured-vuggy reservoirs. Background Technology

[0002] my country possesses abundant carbonate oil and gas resources, with estimated petroleum geological resources of approximately 34 billion tons. Fractured-vuggy reservoirs are a crucial component of these resources. The reservoir space in fractured-vuggy reservoirs is a composite reservoir of fractures and caverns, formed by multiple phases of faulting and fluid dissolution. Fractures and caverns serve as the primary flow channels and storage spaces for oil and gas, respectively, controlling the multiphase fluid flow processes and oil and gas production within the reservoir. However, the highly heterogeneous fracture-vuggy structure in these reservoirs leads to complex water and gas injection displacement processes, making it difficult to predict remaining oil distribution and adjust development plans. Therefore, accurate characterization of fracture flow channels and cavern structures in fractured-vuggy reservoirs is essential for efficient oil and gas development.

[0003] Current characterization of fractured-vuggy reservoirs primarily relies on geophysical data such as seismic and well logging. However, due to limitations in the resolution of geophysical techniques at deep burial sites, the accuracy of the established fractured-vuggy reservoir models is often limited, making it difficult to accurately identify and describe the internal pore-fracture-vuggy combinations. Furthermore, fluids often have dominant flow channels within fractured-vuggy networks, and some seemingly connected fractures may close due to filling or compressive stress, creating a "false connectivity" phenomenon. Relying solely on geological information can easily lead to misjudgments of the interconnected structure of fractured-vuggy reservoirs. In contrast, hydraulic parameter inversion methods are unaffected by reservoir depth. They rely on forward modeling methods, combined with optimization algorithms to automatically fit production dynamic data, achieving inversion characterization of flow channel structure and properties. However, they are affected by the complex flow patterns within fractured-vuggy reservoirs—i.e., the matrix and fractures exhibit multiphase seepage, while caverns exhibit multiphase free flow—making numerical simulation of fractured-vuggy reservoirs highly difficult and complex. Moreover, current hydraulic parameter inversion methods typically ignore the constraints of existing geological, seismic exploration, tracing, and well testing information, resulting in significant deviations between the inversion results and actual geological conditions, leading to poor predictability and guidance for future production. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for inverting flow channels and cavern structures in fractured-vuggy reservoirs.

[0005] The objective of this invention is achieved through the following technical solution: a method for inverting flow channels and cavern structures in fractured-vuggy reservoirs, comprising the following steps:

[0006] S1: Establish a mathematical model of three-phase multi-component flow of oil, gas and water in fractured and vulcanized reservoirs, and obtain a numerical simulation method for fluid flow in fractured and vulcanized reservoirs;

[0007] S2: Construct the inversion variable space and establish the production dynamic fitting objective function;

[0008] S3: Extract multi-source data constraint information and perform flow channel and karst cave structure inversion based on the multi-source data constraint information.

[0009] Preferably, step S1 further includes the following step:

[0010] S11: The continuity equation of fluid flow in the matrix, fracture and cavern system is established in the form of three-phase multi-component oil, gas and water, and the fluid exchange between different media is associated with the quasi-steady-state crossflow term.

[0011] S12: Based on Darcy's law for multiphase flow, the three-phase multi-component flow velocity of oil, gas, and water in the matrix and fractures is described by the following equation:

[0012] ;

[0013] ;

[0014] in, For seepage velocity, Viscosity, This refers to relative penetration rate. This refers to the reservoir depth.

[0015] S13: Perform phase equilibrium model of oil and gas phase transformation and property calculation based on Peng-Robinson equation of state, perform water phase property calculation based on equation of state of pressure and compressibility coefficient, and establish auxiliary equations;

[0016] S14: The reservoir region is meshed using a structured grid, and the natural fracture network in the reservoir is processed by an embedded discrete fracture model to merge all the grids in the cavern region to form a cavern body;

[0017] S15: Based on the finite volume method, the mathematical model of three-phase multi-component flow of oil, gas and water is numerically discretized, and a fully implicit iterative solution scheme is constructed by Newton's iteration method to obtain a numerical simulation method for fluid flow in fractured and vulcanized reservoirs.

[0018] Preferably, in step S11, the fluid continuity equation of the reservoir matrix system is:

[0019] ;

[0020] ;

[0021] The continuity equation for fluid flow in a fracture system is:

[0022] ;

[0023] ;

[0024] The continuity equation for fluid flow in a cave system is:

[0025] ;

[0026] ;

[0027] Among them, subscript , , It consists of three phases: oil, gas, and water. , , These are the matrix, fissures, and cave systems, respectively. Hydrocarbons Mole fraction of the component in the oil phase Hydrocarbons Mole fraction of the component in the gas phase. molar density, For saturation, For reservoir porosity, Hydrocarbons Source and sink terms of components For the source and sink of water components, This refers to the fluid flow term between the matrix and the fracture system. This refers to the fluid flow term between the matrix and the cave system. This refers to the fluid flow term between the fissure and cave system.

[0028] Preferably, step S2 further includes the following step:

[0029] S21: The reservoir in the inter-well profile is divided into a structured grid, and inversion variables of fracture-vuggy structure are established on the grid, including discrete variables and continuous variables;

[0030] S22: Using production data as fitting data, constructing a posterior probability density distribution function based on Bayes' theorem, and extracting the objective function of the inverse problem based on maximizing the posterior probability density distribution function;

[0031] S23: Obtain the inversion results of flow channels and karst cave structures based on objective functions of discrete and continuous variables.

[0032] Preferably, in step S21, there are four inversion variables on each grid, namely, cave identifier, cave volume factor, local flow channel direction, and flow channel conductivity.

[0033] Preferably, in step S22, the distribution functions of discrete variables for cave identification and local flow channel direction, as well as the distribution functions of continuous variables for cave volume coefficient and flow channel conductivity, are constructed based on Bayes' theorem.

[0034] Preferably, in step S22, the objective function for the discrete variables is:

[0035] ;

[0036] The objective function for continuous variables is:

[0037] ;

[0038] in, It is a discrete variable vector that includes cave identifiers and the direction of local flow channels. It is a continuous variable vector containing the conductivity of the flow channels and the volume coefficient of the karst cave. For prior information about variables, The covariance matrix of the production dynamic data, Let covariance be the matrix of discrete variables. The covariance matrix of continuous variables, For monitoring production dynamic data, These are the results of the numerical simulation.

[0039] Preferably, step S23 further includes the following step:

[0040] S23.1: With fixed initial attribute values, the Gauss-Newton iteration method is used to iteratively invert the cave identifiers and local flow channel directions to obtain the optimal flow channels and cave spatial distribution;

[0041] S23.2: Based on the optimal flow channels and spatial distribution of karst caves, the Gauss-Newton iteration method is used to invert the volume coefficient of karst caves and the conductivity of flow channels, and the inversion results of flow channels and karst cave structures are obtained comprehensively.

[0042] Preferably, step S3 further includes the following step:

[0043] S31: Based on the orientation, dip angle, location, opening and density information of the intersecting fractures in the wellbore, establish a near-wellbore flow channel model;

[0044] S32: Based on the inter-well tracer test results, obtain the connectivity information of different layers between wells, and construct the covariance matrix of the local flow channel direction variables accordingly;

[0045] S33: Convert the structural tensor seismic data into a grayscale spatial distribution, extract the structural features of the karst cave based on the grayscale distribution, and construct the covariance matrix of the karst cave identifier variable through smoothing matrix transformation;

[0046] S34: Establish an initial model of flow channels and caverns in fractured-collapse reservoirs based on near-wellbore flow channel models and fractured-cavity structures;

[0047] S35: Integrate the above constraint information into the flow channel and karst cave structure inversion method to form the flow channel and karst cave structure inversion method.

[0048] The present invention has the following advantages: The present invention can not only explain the geometric structure of flow channels and karst caves in fractured-vuggy reservoirs, but also explain the flow properties of flow channels and the effective volume space of karst caves, realize the dynamic connectivity analysis of flow channels and karst cave structures in fractured-vuggy reservoirs, and provide scientific basis for developers through the explanation of flow channel and karst cave structure and properties, enabling efficient development of fractured-vuggy oil and gas reservoirs. Attached Figure Description

[0049] Figure 1 A schematic diagram of the process for inverting flow channels and cavern structures in fractured-vuggy reservoirs;

[0050] Figure 2 This is a schematic diagram of an instantaneous gravity differentiation model for multiphase fluids in a karst cave.

[0051] Figure 3 This is a schematic diagram illustrating the principle of inversion between flow channels and karst cave structures.

[0052] Figure 4 A schematic diagram for extracting flow channel constraint information from near-wellbore observation data;

[0053] Figure 5 A schematic diagram for extracting cave structure constraint information from seismic data. Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0055] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0056] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other.

[0057] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0058] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use, or the orientation or positional relationship commonly understood by those skilled in the art. They are only used for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. In addition, the terms "first," "second," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0059] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0060] In this embodiment, as Figure 1 As shown, a method for inverting flow channels and cavern structures in fractured-vuggy reservoirs includes the following steps:

[0061] S1: Establish a mathematical model for the three-phase multi-component flow of oil, gas and water in fractured-vuggy reservoirs, and obtain a numerical simulation method for fluid flow in fractured-vuggy reservoirs; specifically, considering the coupling effect of matrix-fracture seepage and cavern free flow, establish a mathematical model for the three-phase multi-component flow of oil, gas and water in fractured-vuggy reservoirs, and combine it with embedded discrete fractures and a multiphase fluid instantaneous gravity differentiation model to construct a numerical simulation method for fluid flow in fractured-vuggy reservoirs.

[0062] S2: Construct the inversion variable space and establish the production dynamic fitting objective function;

[0063] S3: Extract multi-source data constraint information and perform flow channel and cavern structure inversion based on this information. This not only explains the geometric structure of flow channels and caverns in fractured-vuggy reservoirs, but also the flow properties of flow channels and the effective volume space of caverns. It enables dynamic connectivity analysis of flow channels and cavern structures in fractured-vuggy reservoirs. Furthermore, the interpretation of flow channel and cavern structure and properties provides developers with a scientific basis for the efficient development of fractured-vuggy oil and gas reservoirs.

[0064] Furthermore, such as Figure 2 As shown, step S1 also includes the following steps:

[0065] S11: A continuity equation for fluid flow in the matrix, fracture, and cavern systems is established using a three-phase, multi-component approach involving oil, gas, and water. A quasi-steady-state channeling term is used to correlate fluid exchange between different media. Specifically, the fluid continuity equation for the reservoir matrix system is:

[0066] ;

[0067] ;

[0068] The continuity equation for fluid flow in a fracture system is:

[0069] ;

[0070] ;

[0071] The continuity equation for fluid flow in a cave system is:

[0072] ;

[0073] ;

[0074] Among them, subscript , , It consists of three phases: oil, gas, and water. , , These are the matrix, fissures, and cave systems, respectively. Hydrocarbons Mole fraction of the component in the oil phase Hydrocarbons Mole fraction of the component in the gas phase. molar density, For saturation, For reservoir porosity, Hydrocarbons Source and sink terms of components For the source and sink of water components, This refers to the fluid flow term between the matrix and the fracture system. This refers to the fluid flow term between the matrix and the cave system. This refers to the fluid flow term between the fissure and cave system.

[0075] S12: Based on Darcy's law for multiphase flow, the three-phase multi-component flow velocity of oil, gas, and water in the matrix and fractures is described by the following equation:

[0076] ;

[0077] ;

[0078] in, For seepage velocity, Viscosity, This refers to relative penetration rate. The depth is defined as the reservoir depth. Specifically, here the karst cave is set as an equipotential body, the oil and gas in the karst cave are in instantaneous thermodynamic phase equilibrium, and the free flow of oil, gas and water is treated by multiphase fluid instantaneous gravity differentiation.

[0079] S13: Perform phase equilibrium model of oil and gas phase transformation and property calculation based on Peng-Robinson equation of state, perform water phase property calculation based on equation of state of pressure and compressibility coefficient, and establish auxiliary equations;

[0080] S14: The reservoir region is meshed using a structured grid, and the natural fracture network in the reservoir is processed by an embedded discrete fracture model. All grids in the cavern region are merged to form a cavern body. That is, each grid corresponds to a control volume, and variables such as pressure, saturation and component mole fraction are all located at the center of the grid.

[0081] S15: Based on the finite volume method, the mathematical model of three-phase multi-component flow of oil, gas and water is numerically discretized, and a fully implicit iterative solution scheme is constructed by Newton's iteration method to obtain a numerical simulation method for fluid flow in fractured and vulcanized reservoirs.

[0082] In this embodiment, as Figure 3 As shown, step S2 also includes the following steps:

[0083] S21: The reservoir profile between wells is divided into structured grids, and inversion variables for fracture-vuggy structure are established on the grids, including discrete and continuous variables. Furthermore, each grid contains four inversion variables: vuggy identification, vuggy volume factor, local flow channel direction, and flow channel conductivity. Specifically, vuggy identification and local flow channel direction are discrete variables reflecting the spatial distribution of flow channels and vuggies. Vuggy identification includes two states: whether it is a vuggy region or not, and local flow channel direction includes six states. Vuggy volume factor and flow channel conductivity are continuous variables reflecting the size of the vuggy reservoir space and the conductivity properties of the flow channels.

[0084] S22: Using production data as fitting data, a posterior probability density distribution function is constructed based on Bayes' theorem, and the objective function of the inverse problem is extracted by maximizing the posterior probability density distribution function. Specifically, based on Bayes' theorem, distribution functions are constructed for discrete variables such as cave identification and local flow channel direction, as well as for continuous variables such as cave volume coefficient and flow channel conductivity. Furthermore, the objective function for the discrete variables is:

[0085] ;

[0086] The objective function for continuous variables is:

[0087] ;

[0088] in, It is a discrete variable vector that includes cave identifiers and the direction of local flow channels. It is a continuous variable vector containing the conductivity of the flow channels and the volume coefficient of the karst cave. For prior information about variables, The covariance matrix of the production dynamic data, Let covariance be the matrix of discrete variables. The covariance matrix of continuous variables, For monitoring production dynamic data, These are the results of the numerical simulation.

[0089] S23: Obtain the inversion results of the flow channels and karst cave structures based on the objective function of discrete and continuous variables. Specifically, step S23 also includes the following steps:

[0090] S23.1: With fixed initial attribute values, the Gauss-Newton iteration method is used to iteratively invert the cave identifiers and local flow channel directions to obtain the optimal flow channels and cave spatial distribution;

[0091] S23.2: Based on the optimal flow channels and spatial distribution of karst caves, the Gauss-Newton iteration method is used to invert the volume coefficient of karst caves and the conductivity of flow channels, and the inversion results of flow channels and karst cave structures are obtained comprehensively.

[0092] In this embodiment, as Figure 4 and Figure 5 As shown, step S3 also includes the following steps:

[0093] S31: Based on the orientation, dip angle, location, opening and density information of intersecting fractures in the wellbore, establish a near-wellbore flow channel model, which serves as a rigid constraint for the inverse evolution of the flow channel; specifically, based on wellbore observation data such as drilling core observation and imaging logging, statistically analyze the orientation, dip angle, location, opening and density information of intersecting fractures in the wellbore.

[0094] S32: Based on the inter-well tracer test results, obtain the connectivity information of different layers between wells, and construct the covariance matrix of the local flow channel direction variables accordingly;

[0095] S33: Based on image processing technology, structural tensor seismic data is converted into grayscale spatial distribution, and the structural features of karst caves are extracted based on the grayscale distribution. The covariance matrix of the karst cave identifier variable is constructed through smooth matrix transformation.

[0096] S34: Establish an initial model of flow channels and karst caves in fractured-dissolved reservoirs based on near-wellbore flow channel models and fractured-cavity structures; specifically, establish flow channel and karst cave models in fractured-dissolved reservoirs based on near-wellbore flow channels established from drilling and imaging logging information and fractured-cavity structures established from inter-well data, thereby providing an initial model that conforms to geological understanding for hydraulic parameter inversion.

[0097] S35: Integrate the above constraint information into the flow channel and karst cave structure inversion method to form the flow channel and karst cave structure inversion method.

[0098] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method of fracture-vug reservoir flow path and vug structure inversion, characterized by: Includes the following steps: S1: Establish a mathematical model of three-phase multi-component flow of oil, gas and water in fractured and vulcanized reservoirs, and obtain a numerical simulation method for fluid flow in fractured and vulcanized reservoirs; S2: Construct the inversion variable space and establish the production dynamic fitting objective function; S3: Extract multi-source data constraint information and perform flow channel and karst cave structure inversion based on multi-source data constraint information; Step S2 further includes the following steps: S21: The reservoir in the inter-well profile is divided into a structured grid, and inversion variables of fracture-vuggy structure are established on the grid, including discrete variables and continuous variables; S22: Using production data as fitting data, constructing a posterior probability density distribution function based on Bayes' theorem, and extracting the objective function of the inverse problem based on maximizing the posterior probability density distribution function; S23: Obtaining the inversion results of flow channels and karst cave structures based on objective functions of discrete and continuous variables; In step S22, based on Bayes' theorem, the distribution functions of discrete variables of cave identification and local flow channel direction, as well as the distribution functions of continuous variables of cave volume coefficient and flow channel conductivity, are constructed respectively. Step S3 further includes the following steps: S31: Based on the orientation, dip angle, location, opening and density information of the intersecting fractures in the wellbore, establish a near-wellbore flow channel model; S32: Based on the inter-well tracer test results, obtain the connectivity information of different layers between wells, and construct the covariance matrix of the local flow channel direction variables accordingly; S33: Convert the structural tensor seismic data into a grayscale spatial distribution, extract the structural features of the karst cave based on the grayscale distribution, and construct the covariance matrix of the karst cave identifier variable through smoothing matrix transformation; S34: Establish an initial model of flow channels and caverns in fractured-collapse reservoirs based on near-wellbore flow channel models and fractured-cavity structures; S35: Integrate the above constraint information into the flow channel and karst cave structure inversion method to form the flow channel and karst cave structure inversion method.

2. The fracture-vug reservoir flow conduit and vug architecture inversion method according to claim 1, wherein: Step S1 further includes the following steps: S11: The continuity equation of fluid flow in the matrix, fracture and cavern system is established in the form of three-phase multi-component oil, gas and water, and the fluid exchange between different media is associated with the quasi-steady-state crossflow term. S12: Based on Darcy's law for multiphase flow, the three-phase multi-component flow velocity of oil, gas, and water in the matrix and fractures is described by the following equation: ； ； wherein, is the seepage velocity, is the viscosity, is the relative permeability, is the reservoir depth; S13: Perform phase equilibrium model of oil and gas phase transformation and property calculation based on Peng-Robinson equation of state, perform water phase property calculation based on equation of state of pressure and compressibility coefficient, and establish auxiliary equations; S14: The reservoir region is meshed using a structured grid, and the natural fracture network in the reservoir is processed by an embedded discrete fracture model to merge all the grids in the cavern region to form a cavern body; S15: Based on the finite volume method, the mathematical model of three-phase multi-component flow of oil, gas and water is numerically discretized, and a fully implicit iterative solution scheme is constructed by Newton's iteration method to obtain a numerical simulation method for fluid flow in fractured and vulcanized reservoirs.

3. The method of claim 2, wherein: In step S11, the fluid continuity equation of the reservoir matrix system is: ； ； The continuity equation for fluid flow in a fracture system is: ； ； The continuity equation for fluid flow in a cave system is: ； ； Among them, subscript , , It consists of three phases: oil, gas, and water. , , These are the matrix, fissures, and cave systems, respectively. Hydrocarbons Mole fraction of the component in the oil phase Hydrocarbons Mole fraction of the component in the gas phase. molar density, For saturation, For reservoir porosity, Hydrocarbons Source and sink terms of components For the source and sink of water components, This refers to the fluid flow term between the matrix and the fracture system. This refers to the fluid flow term between the matrix and the cave system. This refers to the fluid flow term between the fissure and cave system.

4. The method of claim 3, wherein: In step S21, there are four inversion variables on each grid, namely, cave identifier, cave volume coefficient, local flow channel direction, and flow channel conductivity.

5. The method of claim 4, wherein: In step S22, the objective function for the discrete variables is: ； The objective function for continuous variables is: ； wherein, is a discrete variable vector containing cave identification, local flow path direction, is a continuous variable vector containing flow path transmissivity, cave volume fraction, is the prior information of the variables, is the covariance matrix of the production dynamic data, is the covariance matrix of the discrete variables, is the covariance matrix of the continuous variables, is the monitored production dynamic data, is the numerical simulation result.

6. The method of claim 5, wherein: Step S23 further includes the following steps: S23.1: With fixed initial attribute values, the Gauss-Newton iteration method is used to iteratively invert the cave identifiers and local flow channel directions to obtain the optimal flow channels and cave spatial distribution; S23.2: Based on the optimal flow channels and spatial distribution of karst caves, the Gauss-Newton iteration method is used to invert the volume coefficient of karst caves and the conductivity of flow channels, and the inversion results of flow channels and karst cave structures are obtained comprehensively.

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